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HTTP/1.1, part 3: Message Payload and Content NegotiationDay Software23 Corporate Plaza DR, Suite 280Newport BeachCA92660USA+1-949-706-5300+1-949-706-5305fielding@gbiv.comhttp://roy.gbiv.com/One Laptop per Child21 Oak Knoll RoadCarlisleMA01741USAjg@laptop.orghttp://www.laptop.org/Hewlett-Packard CompanyHP Labs, Large Scale Systems Group1501 Page Mill Road, MS 1177Palo AltoCA94304USAJeffMogul@acm.orgMicrosoft Corporation1 Microsoft WayRedmondWA98052USAhenrikn@microsoft.comAdobe Systems, Incorporated345 Park AveSan JoseCA95110USALMM@acm.orghttp://larry.masinter.net/Microsoft Corporation1 Microsoft WayRedmondWA98052paulle@microsoft.comWorld Wide Web ConsortiumMIT Computer Science and Artificial Intelligence LaboratoryThe Stata Center, Building 3232 Vassar StreetCambridgeMA02139USAtimbl@w3.orghttp://www.w3.org/People/Berners-Lee/World Wide Web ConsortiumW3C / ERCIM2004, rte des LuciolesSophia-AntipolisAM06902Franceylafon@w3.orghttp://www.raubacapeu.net/people/yves/greenbytes GmbHHafenweg 16MuensterNW48155Germany+49 251 2807760+49 251 2807761julian.reschke@greenbytes.dehttp://greenbytes.de/tech/webdav/
The Hypertext Transfer Protocol (HTTP) is an application-level
protocol for distributed, collaborative, hypermedia information
systems. HTTP has been in use by the World Wide Web global information
initiative since 1990. This document is Part 3 of the seven-part specification
that defines the protocol referred to as "HTTP/1.1" and, taken together,
obsoletes RFC 2616. Part 3 defines HTTP message content,
metadata, and content negotiation.
Discussion of this draft should take place on the HTTPBIS working group
mailing list (ietf-http-wg@w3.org). The current issues list is
at
and related documents (including fancy diffs) can be found at
.
This document will define aspects of HTTP related to the payload of
messages (message content), including metadata and media types, along
with HTTP content negotiation. Right now it only includes the extracted
relevant sections of RFC 2616 without edit.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in .
An implementation is not compliant if it fails to satisfy one or more
of the &MUST; or &REQUIRED; level requirements for the protocols it
implements. An implementation that satisfies all the &MUST; or &REQUIRED;
level and all the &SHOULD; level requirements for its protocols is said
to be "unconditionally compliant"; one that satisfies all the &MUST;
level requirements but not all the &SHOULD; level requirements for its
protocols is said to be "conditionally compliant."
HTTP uses the same definition of the term "character set" as that
described for MIME:
The term "character set" is used in this document to refer to a
method used with one or more tables to convert a sequence of octets
into a sequence of characters. Note that unconditional conversion in
the other direction is not required, in that not all characters may
be available in a given character set and a character set may provide
more than one sequence of octets to represent a particular character.
This definition is intended to allow various kinds of character
encoding, from simple single-table mappings such as US-ASCII to
complex table switching methods such as those that use ISO-2022's
techniques. However, the definition associated with a MIME character
set name &MUST; fully specify the mapping to be performed from octets
to characters. In particular, use of external profiling information
to determine the exact mapping is not permitted.
Note: This use of the term "character set" is more commonly
referred to as a "character encoding." However, since HTTP and
MIME share the same registry, it is important that the terminology
also be shared.
HTTP character sets are identified by case-insensitive tokens. The
complete set of tokens is defined by the IANA Character Set registry
().
charset = token
Although HTTP allows an arbitrary token to be used as a charset
value, any token that has a predefined value within the IANA
Character Set registry &MUST; represent the character set defined
by that registry. Applications &SHOULD; limit their use of character
sets to those defined by the IANA registry.
HTTP uses charset in two contexts: within an Accept-Charset request
header (in which the charset value is an unquoted token) and as the
value of a parameter in a Content-Type header (within a request or
response), in which case the parameter value of the charset parameter
may be quoted.
Implementors should be aware of IETF character set requirements .
Some HTTP/1.0 software has interpreted a Content-Type header without
charset parameter incorrectly to mean "recipient should guess."
Senders wishing to defeat this behavior &MAY; include a charset
parameter even when the charset is ISO-8859-1 () and &SHOULD; do so when
it is known that it will not confuse the recipient.
Unfortunately, some older HTTP/1.0 clients did not deal properly with
an explicit charset parameter. HTTP/1.1 recipients &MUST; respect the
charset label provided by the sender; and those user agents that have
a provision to "guess" a charset &MUST; use the charset from the
content-type field if they support that charset, rather than the
recipient's preference, when initially displaying a document. See
.
Content coding values indicate an encoding transformation that has
been or can be applied to an entity. Content codings are primarily
used to allow a document to be compressed or otherwise usefully
transformed without losing the identity of its underlying media type
and without loss of information. Frequently, the entity is stored in
coded form, transmitted directly, and only decoded by the recipient.
content-coding = token
All content-coding values are case-insensitive. HTTP/1.1 uses
content-coding values in the Accept-Encoding () and
Content-Encoding () header fields. Although the value
describes the content-coding, what is more important is that it
indicates what decoding mechanism will be required to remove the
encoding.
The Internet Assigned Numbers Authority (IANA) acts as a registry for
content-coding value tokens. Initially, the registry contains the
following tokens:
gzip
An encoding format produced by the file compression program
"gzip" (GNU zip) as described in . This format is a
Lempel-Ziv coding (LZ77) with a 32 bit CRC.
compress
The encoding format produced by the common UNIX file compression
program "compress". This format is an adaptive Lempel-Ziv-Welch
coding (LZW).
Use of program names for the identification of encoding formats
is not desirable and is discouraged for future encodings. Their
use here is representative of historical practice, not good
design. For compatibility with previous implementations of HTTP,
applications &SHOULD; consider "x-gzip" and "x-compress" to be
equivalent to "gzip" and "compress" respectively.
deflate
The "zlib" format defined in in combination with
the "deflate" compression mechanism described in .
identity
The default (identity) encoding; the use of no transformation
whatsoever. This content-coding is used only in the Accept-Encoding
header, and &SHOULD-NOT; be used in the Content-Encoding
header.
New content-coding value tokens &SHOULD; be registered; to allow
interoperability between clients and servers, specifications of the
content coding algorithms needed to implement a new value &SHOULD; be
publicly available and adequate for independent implementation, and
conform to the purpose of content coding defined in this section.
HTTP uses Internet Media Types in the Content-Type ()
and Accept () header fields in order to provide
open and extensible data typing and type negotiation.
media-type = type "/" subtype *( ";" parameter )
type = token
subtype = token
Parameters &MAY; follow the type/subtype in the form of attribute/value
pairs.
parameter = attribute "=" value
attribute = token
value = token | quoted-string
The type, subtype, and parameter attribute names are case-insensitive.
Parameter values might or might not be case-sensitive,
depending on the semantics of the parameter name. Linear white space
(LWS) &MUST-NOT; be used between the type and subtype, nor between an
attribute and its value. The presence or absence of a parameter might
be significant to the processing of a media-type, depending on its
definition within the media type registry.
Note that some older HTTP applications do not recognize media type
parameters. When sending data to older HTTP applications,
implementations &SHOULD; only use media type parameters when they are
required by that type/subtype definition.
Media-type values are registered with the Internet Assigned Number
Authority (IANA). The media type registration process is
outlined in . Use of non-registered media types is
discouraged.
Internet media types are registered with a canonical form. An
entity-body transferred via HTTP messages &MUST; be represented in the
appropriate canonical form prior to its transmission except for
"text" types, as defined in the next paragraph.
When in canonical form, media subtypes of the "text" type use CRLF as
the text line break. HTTP relaxes this requirement and allows the
transport of text media with plain CR or LF alone representing a line
break when it is done consistently for an entire entity-body. HTTP
applications &MUST; accept CRLF, bare CR, and bare LF as being
representative of a line break in text media received via HTTP. In
addition, if the text is represented in a character set that does not
use octets 13 and 10 for CR and LF respectively, as is the case for
some multi-byte character sets, HTTP allows the use of whatever octet
sequences are defined by that character set to represent the
equivalent of CR and LF for line breaks. This flexibility regarding
line breaks applies only to text media in the entity-body; a bare CR
or LF &MUST-NOT; be substituted for CRLF within any of the HTTP control
structures (such as header fields and multipart boundaries).
If an entity-body is encoded with a content-coding, the underlying
data &MUST; be in a form defined above prior to being encoded.
The "charset" parameter is used with some media types to define the
character set () of the data. When no explicit charset
parameter is provided by the sender, media subtypes of the "text"
type are defined to have a default charset value of "ISO-8859-1" when
received via HTTP. Data in character sets other than "ISO-8859-1" or
its subsets &MUST; be labeled with an appropriate charset value. See
for compatibility problems.
MIME provides for a number of "multipart" types -- encapsulations of
one or more entities within a single message-body. All multipart
types share a common syntax, as defined in ,
and &MUST; include a boundary parameter as part of the media type
value. The message body is itself a protocol element and &MUST;
therefore use only CRLF to represent line breaks between body-parts.
Unlike in RFC 2046, the epilogue of any multipart message &MUST; be
empty; HTTP applications &MUST-NOT; transmit the epilogue (even if the
original multipart contains an epilogue). These restrictions exist in
order to preserve the self-delimiting nature of a multipart message-body,
wherein the "end" of the message-body is indicated by the
ending multipart boundary.
In general, HTTP treats a multipart message-body no differently than
any other media type: strictly as payload. The one exception is the
"multipart/byteranges" type (&multipart-byteranges;) when it appears in a 206
(Partial Content) response.
In all
other cases, an HTTP user agent &SHOULD; follow the same or similar
behavior as a MIME user agent would upon receipt of a multipart type.
The MIME header fields within each body-part of a multipart message-body
do not have any significance to HTTP beyond that defined by
their MIME semantics.
In general, an HTTP user agent &SHOULD; follow the same or similar
behavior as a MIME user agent would upon receipt of a multipart type.
If an application receives an unrecognized multipart subtype, the
application &MUST; treat it as being equivalent to "multipart/mixed".
Note: The "multipart/form-data" type has been specifically defined
for carrying form data suitable for processing via the POST
request method, as described in .
HTTP content negotiation () uses short "floating point"
numbers to indicate the relative importance ("weight") of various
negotiable parameters. A weight is normalized to a real number in
the range 0 through 1, where 0 is the minimum and 1 the maximum
value. If a parameter has a quality value of 0, then content with
this parameter is `not acceptable' for the client. HTTP/1.1
applications &MUST-NOT; generate more than three digits after the
decimal point. User configuration of these values &SHOULD; also be
limited in this fashion.
qvalue = ( "0" [ "." 0*3DIGIT ] )
| ( "1" [ "." 0*3("0") ] )
"Quality values" is a misnomer, since these values merely represent
relative degradation in desired quality.
A language tag identifies a natural language spoken, written, or
otherwise conveyed by human beings for communication of information
to other human beings. Computer languages are explicitly excluded.
HTTP uses language tags within the Accept-Language and Content-Language
fields.
The syntax and registry of HTTP language tags is the same as that
defined by . In summary, a language tag is composed of 1
or more parts: A primary language tag and a possibly empty series of
subtags:
language-tag = primary-tag *( "-" subtag )
primary-tag = 1*8ALPHA
subtag = 1*8ALPHA
White space is not allowed within the tag and all tags are case-insensitive.
The name space of language tags is administered by the
IANA. Example tags include:
en, en-US, en-cockney, i-cherokee, x-pig-latin
where any two-letter primary-tag is an ISO-639 language abbreviation
and any two-letter initial subtag is an ISO-3166 country code. (The
last three tags above are not registered tags; all but the last are
examples of tags which could be registered in future.)
Request and Response messages &MAY; transfer an entity if not otherwise
restricted by the request method or response status code. An entity
consists of entity-header fields and an entity-body, although some
responses will only include the entity-headers.
In this section, both sender and recipient refer to either the client
or the server, depending on who sends and who receives the entity.
Entity-header fields define metainformation about the entity-body or,
if no body is present, about the resource identified by the request.
Some of this metainformation is &OPTIONAL;; some might be &REQUIRED; by
portions of this specification.
entity-header = Allow ; &header-allow;
| Content-Encoding ;
| Content-Language ;
| Content-Length ; &header-content-length;
| Content-Location ;
| Content-MD5 ;
| Content-Range ; &header-content-range;
| Content-Type ;
| Expires ; &header-expires;
| Last-Modified ; &header-last-modified;
| extension-header
extension-header = message-header
The extension-header mechanism allows additional entity-header fields
to be defined without changing the protocol, but these fields cannot
be assumed to be recognizable by the recipient. Unrecognized header
fields &SHOULD; be ignored by the recipient and &MUST; be forwarded by
transparent proxies.
The entity-body (if any) sent with an HTTP request or response is in
a format and encoding defined by the entity-header fields.
entity-body = *OCTET
An entity-body is only present in a message when a message-body is
present, as described in &message-body;. The entity-body is obtained
from the message-body by decoding any Transfer-Encoding that might
have been applied to ensure safe and proper transfer of the message.
When an entity-body is included with a message, the data type of that
body is determined via the header fields Content-Type and Content-Encoding.
These define a two-layer, ordered encoding model:
entity-body := Content-Encoding( Content-Type( data ) )
Content-Type specifies the media type of the underlying data.
Content-Encoding may be used to indicate any additional content
codings applied to the data, usually for the purpose of data
compression, that are a property of the requested resource. There is
no default encoding.
Any HTTP/1.1 message containing an entity-body &SHOULD; include a
Content-Type header field defining the media type of that body. If
and only if the media type is not given by a Content-Type field, the
recipient &MAY; attempt to guess the media type via inspection of its
content and/or the name extension(s) of the URI used to identify the
resource. If the media type remains unknown, the recipient &SHOULD;
treat it as type "application/octet-stream".
The entity-length of a message is the length of the message-body
before any transfer-codings have been applied. &message-length; defines
how the transfer-length of a message-body is determined.
Most HTTP responses include an entity which contains information for
interpretation by a human user. Naturally, it is desirable to supply
the user with the "best available" entity corresponding to the
request. Unfortunately for servers and caches, not all users have the
same preferences for what is "best," and not all user agents are
equally capable of rendering all entity types. For that reason, HTTP
has provisions for several mechanisms for "content negotiation" --
the process of selecting the best representation for a given response
when there are multiple representations available.
Note: This is not called "format negotiation" because the
alternate representations may be of the same media type, but use
different capabilities of that type, be in different languages,
etc.
Any response containing an entity-body &MAY; be subject to negotiation,
including error responses.
There are two kinds of content negotiation which are possible in
HTTP: server-driven and agent-driven negotiation. These two kinds of
negotiation are orthogonal and thus may be used separately or in
combination. One method of combination, referred to as transparent
negotiation, occurs when a cache uses the agent-driven negotiation
information provided by the origin server in order to provide
server-driven negotiation for subsequent requests.
If the selection of the best representation for a response is made by
an algorithm located at the server, it is called server-driven
negotiation. Selection is based on the available representations of
the response (the dimensions over which it can vary; e.g. language,
content-coding, etc.) and the contents of particular header fields in
the request message or on other information pertaining to the request
(such as the network address of the client).
Server-driven negotiation is advantageous when the algorithm for
selecting from among the available representations is difficult to
describe to the user agent, or when the server desires to send its
"best guess" to the client along with the first response (hoping to
avoid the round-trip delay of a subsequent request if the "best
guess" is good enough for the user). In order to improve the server's
guess, the user agent &MAY; include request header fields (Accept,
Accept-Language, Accept-Encoding, etc.) which describe its
preferences for such a response.
Server-driven negotiation has disadvantages:
It is impossible for the server to accurately determine what
might be "best" for any given user, since that would require
complete knowledge of both the capabilities of the user agent
and the intended use for the response (e.g., does the user want
to view it on screen or print it on paper?).
Having the user agent describe its capabilities in every
request can be both very inefficient (given that only a small
percentage of responses have multiple representations) and a
potential violation of the user's privacy.
It complicates the implementation of an origin server and the
algorithms for generating responses to a request.
It may limit a public cache's ability to use the same response
for multiple user's requests.
HTTP/1.1 includes the following request-header fields for enabling
server-driven negotiation through description of user agent
capabilities and user preferences: Accept (), Accept-Charset
(), Accept-Encoding (), Accept-Language
(), and User-Agent (&header-user-agent;). However, an
origin server is not limited to these dimensions and &MAY; vary the
response based on any aspect of the request, including information
outside the request-header fields or within extension header fields
not defined by this specification.
The Vary header field (&header-vary;) can be used to express the parameters the
server uses to select a representation that is subject to server-driven
negotiation.
With agent-driven negotiation, selection of the best representation
for a response is performed by the user agent after receiving an
initial response from the origin server. Selection is based on a list
of the available representations of the response included within the
header fields or entity-body of the initial response, with each
representation identified by its own URI. Selection from among the
representations may be performed automatically (if the user agent is
capable of doing so) or manually by the user selecting from a
generated (possibly hypertext) menu.
Agent-driven negotiation is advantageous when the response would vary
over commonly-used dimensions (such as type, language, or encoding),
when the origin server is unable to determine a user agent's
capabilities from examining the request, and generally when public
caches are used to distribute server load and reduce network usage.
Agent-driven negotiation suffers from the disadvantage of needing a
second request to obtain the best alternate representation. This
second request is only efficient when caching is used. In addition,
this specification does not define any mechanism for supporting
automatic selection, though it also does not prevent any such
mechanism from being developed as an extension and used within
HTTP/1.1.
HTTP/1.1 defines the 300 (Multiple Choices) and 406 (Not Acceptable)
status codes for enabling agent-driven negotiation when the server is
unwilling or unable to provide a varying response using server-driven
negotiation.
Transparent negotiation is a combination of both server-driven and
agent-driven negotiation. When a cache is supplied with a form of the
list of available representations of the response (as in agent-driven
negotiation) and the dimensions of variance are completely understood
by the cache, then the cache becomes capable of performing server-driven
negotiation on behalf of the origin server for subsequent
requests on that resource.
Transparent negotiation has the advantage of distributing the
negotiation work that would otherwise be required of the origin
server and also removing the second request delay of agent-driven
negotiation when the cache is able to correctly guess the right
response.
This specification does not define any mechanism for transparent
negotiation, though it also does not prevent any such mechanism from
being developed as an extension that could be used within HTTP/1.1.
This section defines the syntax and semantics of HTTP/1.1 header fields
related to the payload of messages.
For entity-header fields, both sender and recipient refer to either the
client or the server, depending on who sends and who receives the entity.
The Accept request-header field can be used to specify certain media
types which are acceptable for the response. Accept headers can be
used to indicate that the request is specifically limited to a small
set of desired types, as in the case of a request for an in-line
image.
Accept = "Accept" ":"
#( media-range [ accept-params ] )
media-range = ( "*/*"
| ( type "/" "*" )
| ( type "/" subtype )
) *( ";" parameter )
accept-params = ";" "q" "=" qvalue *( accept-extension )
accept-extension = ";" token [ "=" ( token | quoted-string ) ]
The asterisk "*" character is used to group media types into ranges,
with "*/*" indicating all media types and "type/*" indicating all
subtypes of that type. The media-range &MAY; include media type
parameters that are applicable to that range.
Each media-range &MAY; be followed by one or more accept-params,
beginning with the "q" parameter for indicating a relative quality
factor. The first "q" parameter (if any) separates the media-range
parameter(s) from the accept-params. Quality factors allow the user
or user agent to indicate the relative degree of preference for that
media-range, using the qvalue scale from 0 to 1 (). The
default value is q=1.
Note: Use of the "q" parameter name to separate media type
parameters from Accept extension parameters is due to historical
practice. Although this prevents any media type parameter named
"q" from being used with a media range, such an event is believed
to be unlikely given the lack of any "q" parameters in the IANA
media type registry and the rare usage of any media type
parameters in Accept. Future media types are discouraged from
registering any parameter named "q".
The example
Accept: audio/*; q=0.2, audio/basic
&SHOULD; be interpreted as "I prefer audio/basic, but send me any audio
type if it is the best available after an 80% mark-down in quality."
If no Accept header field is present, then it is assumed that the
client accepts all media types. If an Accept header field is present,
and if the server cannot send a response which is acceptable
according to the combined Accept field value, then the server &SHOULD;
send a 406 (not acceptable) response.
A more elaborate example is
Accept: text/plain; q=0.5, text/html,
text/x-dvi; q=0.8, text/x-c
Verbally, this would be interpreted as "text/html and text/x-c are
the preferred media types, but if they do not exist, then send the
text/x-dvi entity, and if that does not exist, send the text/plain
entity."
Media ranges can be overridden by more specific media ranges or
specific media types. If more than one media range applies to a given
type, the most specific reference has precedence. For example,
Accept: text/*, text/html, text/html;level=1, */*
have the following precedence:
1) text/html;level=1
2) text/html
3) text/*
4) */*
The media type quality factor associated with a given type is
determined by finding the media range with the highest precedence
which matches that type. For example,
Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
text/html;level=2;q=0.4, */*;q=0.5
would cause the following values to be associated:
text/html;level=1 = 1
text/html = 0.7
text/plain = 0.3
image/jpeg = 0.5
text/html;level=2 = 0.4
text/html;level=3 = 0.7
Note: A user agent might be provided with a default set of quality
values for certain media ranges. However, unless the user agent is
a closed system which cannot interact with other rendering agents,
this default set ought to be configurable by the user.
The Accept-Charset request-header field can be used to indicate what
character sets are acceptable for the response. This field allows
clients capable of understanding more comprehensive or special-purpose
character sets to signal that capability to a server which is
capable of representing documents in those character sets.
Accept-Charset = "Accept-Charset" ":"
1#( ( charset | "*" )[ ";" "q" "=" qvalue ] )
Character set values are described in . Each charset &MAY;
be given an associated quality value which represents the user's
preference for that charset. The default value is q=1. An example is
Accept-Charset: iso-8859-5, unicode-1-1;q=0.8
The special value "*", if present in the Accept-Charset field,
matches every character set (including ISO-8859-1) which is not
mentioned elsewhere in the Accept-Charset field. If no "*" is present
in an Accept-Charset field, then all character sets not explicitly
mentioned get a quality value of 0, except for ISO-8859-1, which gets
a quality value of 1 if not explicitly mentioned.
If no Accept-Charset header is present, the default is that any
character set is acceptable. If an Accept-Charset header is present,
and if the server cannot send a response which is acceptable
according to the Accept-Charset header, then the server &SHOULD; send
an error response with the 406 (not acceptable) status code, though
the sending of an unacceptable response is also allowed.
The Accept-Encoding request-header field is similar to Accept, but
restricts the content-codings () that are acceptable in
the response.
Accept-Encoding = "Accept-Encoding" ":"
1#( codings [ ";" "q" "=" qvalue ] )
codings = ( content-coding | "*" )
Examples of its use are:
Accept-Encoding: compress, gzip
Accept-Encoding:
Accept-Encoding: *
Accept-Encoding: compress;q=0.5, gzip;q=1.0
Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0
A server tests whether a content-coding is acceptable, according to
an Accept-Encoding field, using these rules:
If the content-coding is one of the content-codings listed in
the Accept-Encoding field, then it is acceptable, unless it is
accompanied by a qvalue of 0. (As defined in , a
qvalue of 0 means "not acceptable.")The special "*" symbol in an Accept-Encoding field matches any
available content-coding not explicitly listed in the header
field.If multiple content-codings are acceptable, then the acceptable
content-coding with the highest non-zero qvalue is preferred.The "identity" content-coding is always acceptable, unless
specifically refused because the Accept-Encoding field includes
"identity;q=0", or because the field includes "*;q=0" and does
not explicitly include the "identity" content-coding. If the
Accept-Encoding field-value is empty, then only the "identity"
encoding is acceptable.
If an Accept-Encoding field is present in a request, and if the
server cannot send a response which is acceptable according to the
Accept-Encoding header, then the server &SHOULD; send an error response
with the 406 (Not Acceptable) status code.
If no Accept-Encoding field is present in a request, the server &MAY;
assume that the client will accept any content coding. In this case,
if "identity" is one of the available content-codings, then the
server &SHOULD; use the "identity" content-coding, unless it has
additional information that a different content-coding is meaningful
to the client.
Note: If the request does not include an Accept-Encoding field,
and if the "identity" content-coding is unavailable, then
content-codings commonly understood by HTTP/1.0 clients (i.e.,
"gzip" and "compress") are preferred; some older clients
improperly display messages sent with other content-codings. The
server might also make this decision based on information about
the particular user-agent or client.
Note: Most HTTP/1.0 applications do not recognize or obey qvalues
associated with content-codings. This means that qvalues will not
work and are not permitted with x-gzip or x-compress.
The Accept-Language request-header field is similar to Accept, but
restricts the set of natural languages that are preferred as a
response to the request. Language tags are defined in .
Accept-Language = "Accept-Language" ":"
1#( language-range [ ";" "q" "=" qvalue ] )
language-range = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" )
Each language-range &MAY; be given an associated quality value which
represents an estimate of the user's preference for the languages
specified by that range. The quality value defaults to "q=1". For
example,
Accept-Language: da, en-gb;q=0.8, en;q=0.7
would mean: "I prefer Danish, but will accept British English and
other types of English." A language-range matches a language-tag if
it exactly equals the tag, or if it exactly equals a prefix of the
tag such that the first tag character following the prefix is "-".
The special range "*", if present in the Accept-Language field,
matches every tag not matched by any other range present in the
Accept-Language field.
Note: This use of a prefix matching rule does not imply that
language tags are assigned to languages in such a way that it is
always true that if a user understands a language with a certain
tag, then this user will also understand all languages with tags
for which this tag is a prefix. The prefix rule simply allows the
use of prefix tags if this is the case.
The language quality factor assigned to a language-tag by the
Accept-Language field is the quality value of the longest language-range
in the field that matches the language-tag. If no language-range
in the field matches the tag, the language quality factor
assigned is 0. If no Accept-Language header is present in the
request, the server
&SHOULD; assume that all languages are equally acceptable. If an
Accept-Language header is present, then all languages which are
assigned a quality factor greater than 0 are acceptable.
It might be contrary to the privacy expectations of the user to send
an Accept-Language header with the complete linguistic preferences of
the user in every request. For a discussion of this issue, see
.
As intelligibility is highly dependent on the individual user, it is
recommended that client applications make the choice of linguistic
preference available to the user. If the choice is not made
available, then the Accept-Language header field &MUST-NOT; be given in
the request.
Note: When making the choice of linguistic preference available to
the user, we remind implementors of the fact that users are not
familiar with the details of language matching as described above,
and should provide appropriate guidance. As an example, users
might assume that on selecting "en-gb", they will be served any
kind of English document if British English is not available. A
user agent might suggest in such a case to add "en" to get the
best matching behavior.
The Content-Encoding entity-header field is used as a modifier to the
media-type. When present, its value indicates what additional content
codings have been applied to the entity-body, and thus what decoding
mechanisms must be applied in order to obtain the media-type
referenced by the Content-Type header field. Content-Encoding is
primarily used to allow a document to be compressed without losing
the identity of its underlying media type.
Content-Encoding = "Content-Encoding" ":" 1#content-coding
Content codings are defined in . An example of its use is
Content-Encoding: gzip
The content-coding is a characteristic of the entity identified by
the Request-URI. Typically, the entity-body is stored with this
encoding and is only decoded before rendering or analogous usage.
However, a non-transparent proxy &MAY; modify the content-coding if the
new coding is known to be acceptable to the recipient, unless the
"no-transform" cache-control directive is present in the message.
If the content-coding of an entity is not "identity", then the
response &MUST; include a Content-Encoding entity-header ()
that lists the non-identity content-coding(s) used.
If the content-coding of an entity in a request message is not
acceptable to the origin server, the server &SHOULD; respond with a
status code of 415 (Unsupported Media Type).
If multiple encodings have been applied to an entity, the content
codings &MUST; be listed in the order in which they were applied.
Additional information about the encoding parameters &MAY; be provided
by other entity-header fields not defined by this specification.
The Content-Language entity-header field describes the natural
language(s) of the intended audience for the enclosed entity. Note
that this might not be equivalent to all the languages used within
the entity-body.
Content-Language = "Content-Language" ":" 1#language-tag
Language tags are defined in . The primary purpose of
Content-Language is to allow a user to identify and differentiate
entities according to the user's own preferred language. Thus, if the
body content is intended only for a Danish-literate audience, the
appropriate field is
Content-Language: da
If no Content-Language is specified, the default is that the content
is intended for all language audiences. This might mean that the
sender does not consider it to be specific to any natural language,
or that the sender does not know for which language it is intended.
Multiple languages &MAY; be listed for content that is intended for
multiple audiences. For example, a rendition of the "Treaty of
Waitangi," presented simultaneously in the original Maori and English
versions, would call for
Content-Language: mi, en
However, just because multiple languages are present within an entity
does not mean that it is intended for multiple linguistic audiences.
An example would be a beginner's language primer, such as "A First
Lesson in Latin," which is clearly intended to be used by an
English-literate audience. In this case, the Content-Language would
properly only include "en".
Content-Language &MAY; be applied to any media type -- it is not
limited to textual documents.
The Content-Location entity-header field &MAY; be used to supply the
resource location for the entity enclosed in the message when that
entity is accessible from a location separate from the requested
resource's URI. A server &SHOULD; provide a Content-Location for the
variant corresponding to the response entity; especially in the case
where a resource has multiple entities associated with it, and those
entities actually have separate locations by which they might be
individually accessed, the server &SHOULD; provide a Content-Location
for the particular variant which is returned.
Content-Location = "Content-Location" ":"
( absoluteURI | relativeURI )
The value of Content-Location also defines the base URI for the
entity.
The Content-Location value is not a replacement for the original
requested URI; it is only a statement of the location of the resource
corresponding to this particular entity at the time of the request.
Future requests &MAY; specify the Content-Location URI as the request-URI
if the desire is to identify the source of that particular
entity.
A cache cannot assume that an entity with a Content-Location
different from the URI used to retrieve it can be used to respond to
later requests on that Content-Location URI. However, the Content-Location
can be used to differentiate between multiple entities
retrieved from a single requested resource, as described in &caching-neg-resp;.
If the Content-Location is a relative URI, the relative URI is
interpreted relative to the Request-URI.
The meaning of the Content-Location header in PUT or POST requests is
undefined; servers are free to ignore it in those cases.
The Content-MD5 entity-header field, as defined in , is
an MD5 digest of the entity-body for the purpose of providing an
end-to-end message integrity check (MIC) of the entity-body. (Note: a
MIC is good for detecting accidental modification of the entity-body
in transit, but is not proof against malicious attacks.)
Content-MD5 = "Content-MD5" ":" md5-digest
md5-digest = <base64 of 128 bit MD5 digest as per >
The Content-MD5 header field &MAY; be generated by an origin server or
client to function as an integrity check of the entity-body. Only
origin servers or clients &MAY; generate the Content-MD5 header field;
proxies and gateways &MUST-NOT; generate it, as this would defeat its
value as an end-to-end integrity check. Any recipient of the entity-body,
including gateways and proxies, &MAY; check that the digest value
in this header field matches that of the entity-body as received.
The MD5 digest is computed based on the content of the entity-body,
including any content-coding that has been applied, but not including
any transfer-encoding applied to the message-body. If the message is
received with a transfer-encoding, that encoding &MUST; be removed
prior to checking the Content-MD5 value against the received entity.
This has the result that the digest is computed on the octets of the
entity-body exactly as, and in the order that, they would be sent if
no transfer-encoding were being applied.
HTTP extends RFC 1864 to permit the digest to be computed for MIME
composite media-types (e.g., multipart/* and message/rfc822), but
this does not change how the digest is computed as defined in the
preceding paragraph.
There are several consequences of this. The entity-body for composite
types &MAY; contain many body-parts, each with its own MIME and HTTP
headers (including Content-MD5, Content-Transfer-Encoding, and
Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
or Content-Encoding header, it is assumed that the content
of the body-part has had the encoding applied, and the body-part is
included in the Content-MD5 digest as is -- i.e., after the
application. The Transfer-Encoding header field is not allowed within
body-parts.
Conversion of all line breaks to CRLF &MUST-NOT; be done before
computing or checking the digest: the line break convention used in
the text actually transmitted &MUST; be left unaltered when computing
the digest.
Note: while the definition of Content-MD5 is exactly the same for
HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
in which the application of Content-MD5 to HTTP entity-bodies
differs from its application to MIME entity-bodies. One is that
HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
does use Transfer-Encoding and Content-Encoding. Another is that
HTTP more frequently uses binary content types than MIME, so it is
worth noting that, in such cases, the byte order used to compute
the digest is the transmission byte order defined for the type.
Lastly, HTTP allows transmission of text types with any of several
line break conventions and not just the canonical form using CRLF.
The Content-Type entity-header field indicates the media type of the
entity-body sent to the recipient or, in the case of the HEAD method,
the media type that would have been sent had the request been a GET.
Content-Type = "Content-Type" ":" media-type
Media types are defined in . An example of the field is
Content-Type: text/html; charset=ISO-8859-4
Further discussion of methods for identifying the media type of an
entity is provided in .
TBD.
This section is meant to inform application developers, information
providers, and users of the security limitations in HTTP/1.1 as
described by this document. The discussion does not include
definitive solutions to the problems revealed, though it does make
some suggestions for reducing security risks.
Accept request-headers can reveal information about the user to all
servers which are accessed. The Accept-Language header in particular
can reveal information the user would consider to be of a private
nature, because the understanding of particular languages is often
strongly correlated to the membership of a particular ethnic group.
User agents which offer the option to configure the contents of an
Accept-Language header to be sent in every request are strongly
encouraged to let the configuration process include a message which
makes the user aware of the loss of privacy involved.
An approach that limits the loss of privacy would be for a user agent
to omit the sending of Accept-Language headers by default, and to ask
the user whether or not to start sending Accept-Language headers to a
server if it detects, by looking for any Vary response-header fields
generated by the server, that such sending could improve the quality
of service.
Elaborate user-customized accept header fields sent in every request,
in particular if these include quality values, can be used by servers
as relatively reliable and long-lived user identifiers. Such user
identifiers would allow content providers to do click-trail tracking,
and would allow collaborating content providers to match cross-server
click-trails or form submissions of individual users. Note that for
many users not behind a proxy, the network address of the host
running the user agent will also serve as a long-lived user
identifier. In environments where proxies are used to enhance
privacy, user agents ought to be conservative in offering accept
header configuration options to end users. As an extreme privacy
measure, proxies could filter the accept headers in relayed requests.
General purpose user agents which provide a high degree of header
configurability &SHOULD; warn users about the loss of privacy which can
be involved.
, from which the often implemented Content-Disposition
(see ) header in HTTP is derived, has a number of very
serious security considerations. Content-Disposition is not part of
the HTTP standard, but since it is widely implemented, we are
documenting its use and risks for implementors. See
(which updates ) for details.
Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
International Organization for StandardizationHTTP/1.1, part 1: URIs, Connections, and Message ParsingDay Softwarefielding@gbiv.comOne Laptop per Childjg@laptop.orgHewlett-Packard CompanyJeffMogul@acm.orgMicrosoft Corporationhenrikn@microsoft.comAdobe Systems, IncorporatedLMM@acm.orgMicrosoft Corporationpaulle@microsoft.comWorld Wide Web Consortiumtimbl@w3.orgWorld Wide Web Consortiumylafon@w3.orggreenbytes GmbHjulian.reschke@greenbytes.deHTTP/1.1, part 2: Message SemanticsDay Softwarefielding@gbiv.comOne Laptop per Childjg@laptop.orgHewlett-Packard CompanyJeffMogul@acm.orgMicrosoft Corporationhenrikn@microsoft.comAdobe Systems, IncorporatedLMM@acm.orgMicrosoft Corporationpaulle@microsoft.comWorld Wide Web Consortiumtimbl@w3.orgWorld Wide Web Consortiumylafon@w3.orggreenbytes GmbHjulian.reschke@greenbytes.deHTTP/1.1, part 4: Conditional RequestsDay Softwarefielding@gbiv.comOne Laptop per Childjg@laptop.orgHewlett-Packard CompanyJeffMogul@acm.orgMicrosoft Corporationhenrikn@microsoft.comAdobe Systems, IncorporatedLMM@acm.orgMicrosoft Corporationpaulle@microsoft.comWorld Wide Web Consortiumtimbl@w3.orgWorld Wide Web Consortiumylafon@w3.orggreenbytes GmbHjulian.reschke@greenbytes.deHTTP/1.1, part 5: Range Requests and Partial ResponsesDay Softwarefielding@gbiv.comOne Laptop per Childjg@laptop.orgHewlett-Packard CompanyJeffMogul@acm.orgMicrosoft Corporationhenrikn@microsoft.comAdobe Systems, IncorporatedLMM@acm.orgMicrosoft Corporationpaulle@microsoft.comWorld Wide Web Consortiumtimbl@w3.orgWorld Wide Web Consortiumylafon@w3.orggreenbytes GmbHjulian.reschke@greenbytes.deHTTP/1.1, part 6: CachingDay Softwarefielding@gbiv.comOne Laptop per Childjg@laptop.orgHewlett-Packard CompanyJeffMogul@acm.orgMicrosoft Corporationhenrikn@microsoft.comAdobe Systems, IncorporatedLMM@acm.orgMicrosoft Corporationpaulle@microsoft.comWorld Wide Web Consortiumtimbl@w3.orgWorld Wide Web Consortiumylafon@w3.orggreenbytes GmbHjulian.reschke@greenbytes.deZLIB Compressed Data Format Specification version 3.3Aladdin Enterprisesghost@aladdin.com
RFC1950 is an Informational RFC, thus it may be less stable than
this specification. On the other hand, this downward reference was
present since (published in 1997), therefore it is unlikely
to cause problems in practice.
DEFLATE Compressed Data Format Specification version 1.3Aladdin Enterprisesghost@aladdin.com
RFC1951 is an Informational RFC, thus it may be less stable than
this specification. On the other hand, this downward reference was
present since (published in 1997), therefore it is unlikely
to cause problems in practice.
GZIP file format specification version 4.3Aladdin Enterprisesghost@aladdin.comgzip@prep.ai.mit.edumadler@alumni.caltech.edughost@aladdin.comrandeg@alumni.rpi.edu
RFC1952 is an Informational RFC, thus it may be less stable than
this specification. On the other hand, this downward reference was
present since (published in 1997), therefore it is unlikely
to cause problems in practice.
Key words for use in RFCs to Indicate Requirement LevelsHarvard Universitysob@harvard.eduHypertext Transfer Protocol -- HTTP/1.1University of California, Irvine, Department of Information and Computer Sciencefielding@ics.uci.eduMIT Laboratory for Computer Sciencejg@w3.orgDigital Equipment Corporation, Western Research Laboratorymogul@wrl.dec.comMIT Laboratory for Computer Sciencefrystyk@w3.orgMIT Laboratory for Computer Sciencetimbl@w3.orgHypertext Transfer Protocol -- HTTP/1.1University of California, Irvinefielding@ics.uci.eduW3Cjg@w3.orgCompaq Computer Corporationmogul@wrl.dec.comMIT Laboratory for Computer Sciencefrystyk@w3.orgXerox Corporationmasinter@parc.xerox.comMicrosoft Corporationpaulle@microsoft.comW3Ctimbl@w3.orgTags for the Identification of LanguagesUNINETTHarald.T.Alvestrand@uninett.noMultipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message BodiesInnosoft International, Inc.ned@innosoft.comFirst Virtual Holdingsnsb@nsb.fv.comStandard for the format of ARPA Internet text messagesUniversity of Delaware, Dept. of Electrical EngineeringDCrocker@UDel-RelayForm-based File Upload in HTMLXerox Palo Alto Research Centermasinter@parc.xerox.comXSoft, Xerox Corporationnebel@xsoft.sd.xerox.comMedia Type Specifications and Registration ProceduresSun Microsystemsned.freed@mrochek.comklensin+ietf@jck.comThe Content-MD5 Header FieldCarnegie Mellon Universityjgm+@cmu.eduDover Beach Consulting, Inc.mrose@dbc.mtview.ca.usCommunicating Presentation Information in Internet Messages: The Content-Disposition HeaderNew Century Systemsrens@century.comQUALCOMM Incorporatedsdorner@qualcomm.comHypertext Transfer Protocol -- HTTP/1.0MIT, Laboratory for Computer Sciencetimbl@w3.orgUniversity of California, Irvine, Department of Information and Computer Sciencefielding@ics.uci.eduW3 Consortium, MIT Laboratory for Computer Sciencefrystyk@w3.orgCommon Internet Message HeadersStockholm University/KTHjpalme@dsv.su.seUTF-8, a transformation format of ISO 10646Alis Technologies100, boul. Alexis-NihonSuite 600MontrealQuebecH4M 2P2CA+1 514 747 2547+1 514 747 2561fyergeau@alis.comISO/IEC 10646-1 defines a multi-octet character set called the Universal Character Set (UCS) which encompasses most of the world's writing systems. Multi-octet characters, however, are not compatible with many current applications and protocols, and this has led to the development of a few so-called UCS transformation formats (UTF), each with different characteristics. UTF-8, the object of this memo, has the characteristic of preserving the full US-ASCII range, providing compatibility with file systems, parsers and other software that rely on US-ASCII values but are transparent to other values. This memo updates and replaces RFC 2044, in particular addressing the question of versions of the relevant standards.Multipurpose Internet Mail Extensions (MIME) Part Two: Media TypesInnosoft International, Inc.ned@innosoft.comFirst Virtual Holdingsnsb@nsb.fv.comIETF Policy on Character Sets and LanguagesUNINETTP.O.Box 6883 ElgeseterN-7002 TRONDHEIMNORWAY+47 73 59 70 94Harald.T.Alvestrand@uninett.noApplications
Internet Engineering Task Forcecharacter encodingMIME E-mail Encapsulation of Aggregate Documents, such as HTML (MHTML)Stockholm University and KTHElectrum 230S-164 40 KistaSweden+46-8-16 16 67+46-8-783 08 29jpalme@dsv.su.seMicrosoft Corporation3590 North First StreetSuite 300San JoseCA 95134Working group chairman:alexhop@microsoft.comApplications
encapsulatehypertext markup languagemailmultipurpose internet mail extensionsMultipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and ExamplesInnosoft International, Inc.ned@innosoft.comFirst Virtual Holdingsnsb@nsb.fv.comCommunicating Presentation Information in Internet Messages: The Content-Disposition Header FieldNew Century Systemsrens@century.comQUALCOMM Incorporatedsdorner@qualcomm.comDepartment of Computer Sciencemoore@cs.utk.edu
HTTP/1.1 uses many of the constructs defined for Internet Mail () and the Multipurpose Internet Mail Extensions (MIME ) to
allow entities to be transmitted in an open variety of
representations and with extensible mechanisms. However, RFC 2045
discusses mail, and HTTP has a few features that are different from
those described in RFC 2045. These differences were carefully chosen
to optimize performance over binary connections, to allow greater
freedom in the use of new media types, to make date comparisons
easier, and to acknowledge the practice of some early HTTP servers
and clients.
This appendix describes specific areas where HTTP differs from RFC
2045. Proxies and gateways to strict MIME environments &SHOULD; be
aware of these differences and provide the appropriate conversions
where necessary. Proxies and gateways from MIME environments to HTTP
also need to be aware of the differences because some conversions
might be required.
HTTP is not a MIME-compliant protocol. However, HTTP/1.1 messages &MAY;
include a single MIME-Version general-header field to indicate what
version of the MIME protocol was used to construct the message. Use
of the MIME-Version header field indicates that the message is in
full compliance with the MIME protocol (as defined in ).
Proxies/gateways are responsible for ensuring full compliance (where
possible) when exporting HTTP messages to strict MIME environments.
MIME-Version = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT
MIME version "1.0" is the default for use in HTTP/1.1. However,
HTTP/1.1 message parsing and semantics are defined by this document
and not the MIME specification.
requires that an Internet mail entity be converted to
canonical form prior to being transferred, as described in .
of this document describes the forms
allowed for subtypes of the "text" media type when transmitted over
HTTP. requires that content with a type of "text" represent
line breaks as CRLF and forbids the use of CR or LF outside of line
break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
line break within text content when a message is transmitted over
HTTP.
Where it is possible, a proxy or gateway from HTTP to a strict MIME
environment &SHOULD; translate all line breaks within the text media
types described in of this document to the RFC 2049
canonical form of CRLF. Note, however, that this might be complicated
by the presence of a Content-Encoding and by the fact that HTTP
allows the use of some character sets which do not use octets 13 and
10 to represent CR and LF, as is the case for some multi-byte
character sets.
Implementors should note that conversion will break any cryptographic
checksums applied to the original content unless the original content
is already in canonical form. Therefore, the canonical form is
recommended for any content that uses such checksums in HTTP.
RFC 2045 does not include any concept equivalent to HTTP/1.1's
Content-Encoding header field. Since this acts as a modifier on the
media type, proxies and gateways from HTTP to MIME-compliant
protocols &MUST; either change the value of the Content-Type header
field or decode the entity-body before forwarding the message. (Some
experimental applications of Content-Type for Internet mail have used
a media-type parameter of ";conversions=<content-coding>" to perform
a function equivalent to Content-Encoding. However, this parameter is
not part of RFC 2045).
HTTP does not use the Content-Transfer-Encoding field of RFC
2045. Proxies and gateways from MIME-compliant protocols to HTTP &MUST;
remove any Content-Transfer-Encoding
prior to delivering the response message to an HTTP client.
Proxies and gateways from HTTP to MIME-compliant protocols are
responsible for ensuring that the message is in the correct format
and encoding for safe transport on that protocol, where "safe
transport" is defined by the limitations of the protocol being used.
Such a proxy or gateway &SHOULD; label the data with an appropriate
Content-Transfer-Encoding if doing so will improve the likelihood of
safe transport over the destination protocol.
HTTP/1.1 introduces the Transfer-Encoding header field (&header-transfer-encoding;).
Proxies/gateways &MUST; remove any transfer-coding prior to
forwarding a message via a MIME-compliant protocol.
HTTP implementations which share code with MHTML implementations
need to be aware of MIME line length limitations. Since HTTP does not
have this limitation, HTTP does not fold long lines. MHTML messages
being transported by HTTP follow all conventions of MHTML, including
line length limitations and folding, canonicalization, etc., since
HTTP transports all message-bodies as payload (see ) and
does not interpret the content or any MIME header lines that might be
contained therein.
and document protocol elements used by some
existing HTTP implementations, but not consistently and correctly
across most HTTP/1.1 applications. Implementors are advised to be
aware of these features, but cannot rely upon their presence in, or
interoperability with, other HTTP/1.1 applications. Some of these
describe proposed experimental features, and some describe features
that experimental deployment found lacking that are now addressed in
the base HTTP/1.1 specification.
A number of other headers, such as Content-Disposition and Title,
from SMTP and MIME are also often implemented (see ).
The Content-Disposition response-header field has been proposed as a
means for the origin server to suggest a default filename if the user
requests that the content is saved to a file. This usage is derived
from the definition of Content-Disposition in .
content-disposition = "Content-Disposition" ":"
disposition-type *( ";" disposition-parm )
disposition-type = "attachment" | disp-extension-token
disposition-parm = filename-parm | disp-extension-parm
filename-parm = "filename" "=" quoted-string
disp-extension-token = token
disp-extension-parm = token "=" ( token | quoted-string )
An example is
Content-Disposition: attachment; filename="fname.ext"
The receiving user agent &SHOULD-NOT; respect any directory path
information present in the filename-parm parameter, which is the only
parameter believed to apply to HTTP implementations at this time. The
filename &SHOULD; be treated as a terminal component only.
If this header is used in a response with the application/octet-stream
content-type, the implied suggestion is that the user agent
should not display the response, but directly enter a `save response
as...' dialog.
See for Content-Disposition security issues.
Charset wildcarding is introduced to avoid explosion of character set
names in accept headers. ()
Content-Base was deleted from the specification: it was not
implemented widely, and there is no simple, safe way to introduce it
without a robust extension mechanism. In addition, it is used in a
similar, but not identical fashion in MHTML .
A content-coding of "identity" was introduced, to solve problems
discovered in caching. ()
Quality Values of zero should indicate that "I don't want something"
to allow clients to refuse a representation. ()
The Alternates, Content-Version, Derived-From, Link, URI, Public and
Content-Base header fields were defined in previous versions of this
specification, but not commonly implemented. See .
Clarify contexts that charset is used in.
()
Remove reference to non-existant identity transfer-coding value tokens.
()
Extracted relevant partitions from .
Closed issues:
:
"Media Type Registrations"
()
:
"Clarification regarding quoting of charset values"
()
:
"Remove 'identity' token references"
()
:
"RFC1700 references"
:
"ISO-8859-1 Reference"
:
"Encoding References Normative"
Other changes:
Start work on categorizing references as "Normative" or "Informative".